In 1930 Dr Frank Ellis, who has died aged 100, was appointed the first radium officer at the Royal Hospital in Sheffield, shown into an empty, disused operating theatre and left to set up a clinical service. He went on to be a world leader in the treatment of cancer by radiation therapy, and his ideas, energetically developed, mainly in Sheffield and Oxford, led to improvements for patients that still form the basis of modern practice.

At Sheffield in the early 1930s there was much lobbying to be done of the hospital board of governors. He also obtained a stock of radium and other basic equipment and went in search of backing from John Graves, a fellow chapel-goer, and sometime mayor of Sheffield, who financed Metro-Vickers X-ray equipment.

Thus had begun Ellis's lifelong work to discover the best ways in which to deliver a sufficient radiation dose to kill the cells of a malignant tumour, while sparing as far as possible its surrounding normal tissues. At the same time he sought to establish which patients would most benefit from this treatment by working closely with other specialists.

A practical man, Frank had the ability to attract innovative staff to work with him to develop new equipment. In 1935 he developed wooden wedge-shaped filters which, when placed in a radiation beam, allowed the beam to be angled to avoid sensitive normal structures such as the eye. This one idea revolutionised external beam treatment and is still a basic component of modern radiotherapy equipment. He later invented many other devices to improve accuracy and uniformity of the radiation dose.

During the second world war, and the blitz on Sheffield, he was concerned that bombing might not only interfere with his patients' treatment but also risk radioactive contamination. As a consequence he hired a furniture van and moved his department, including the radium, out of Sheffield to a safer location. In those days, direct action was the best way to succeed.

In 1943 Frank became the first director of the radiotherapy department at the Royal London Hospital. In 1950, two years after the foundation of the national health service, he moved to the Churchill hospital in Oxford. There, once again, he set up a department. The location was in huts recently vacated by the American armed forces and he embarked upon the design and construction of the first telecobalt unit, which although very heavy, because of its lead shielding, was capable of both vertical and angular movement. In this he secured the help of HC Husband, the designer of Jodrell Bank Observatory. This equipment treated patients very effectively for 25 years, and was then given to the Science Museum in London.

During his years at Oxford, Frank collected around him a group of enterprising young trainees. Under his guidance they were to contribute hugely to the understanding of the physical and biological basis of radiation therapy. Several went on to head units of renown in Britain and abroad.

Another of his important developments at Oxford was the replacement of radium - a hazardous material - with newer alternatives becoming available from the 1950s. This had great benefits for patients and staff, and also allowed him to pursue the combination of operative surgery with radiotherapy - which he was to develop further in the US. He also established clinics in towns outside Oxford, so saving patients from having to travel.

Frank had been born in Sheffield. His father was a brass finisher and his parents also looked after the local chapel. By the age of five he had decided he wanted to become a doctor. When he was 10 his parents moved across the city and so, in 1915 he was enrolled in Nether Green School. There his headmaster, and crucially his teacher Miss Raby, recognised his ability. She worked closely with him, and he won a scholarship, worth £5 a year, to King Edward VII grammar school. Excelling academically, in 1924 he received his higher school certificate. He was also good at sport - a competitive soccer player and runner and, later in life, a squash player, who regularly defeated his colleagues, older and younger.

To go to Oxford was considered too expensive and so, having won the Styring scholarship he went to Sheffield University medical school. Winning prizes and graduating with honour in 1929, he proposed to his wife to-be, Dorothy Parr - they married in 1932 - and presented a bunch of flowers to Miss Raby.

After that, as he said, he never looked back. Frank had been scheduled to take up a medical appointment in Southern Rhodesia (now Zimbabwe) but an eye infection prevented that. It was while convalescing that a friend suggested he apply for the Sheffield radium post. By the age of 25, he had become a consultant. After six months visiting centres elsewhere, in London, Belgium, Sweden and Germany he took up his appointment on May 1 1931. Soon after he accepted a £5 bet from a young fellow doctor and cycled to London in 24 hours - and then cycled back. Conscious of his friend's poverty, he never cashed the cheque.

Frank's statutory retirement from the NHS at 65 came in 1970. By then his renown in his field was at its highest due to his success in combining his clinical experience with radiobiology to develop the concept of nominal standard dose (NSD). This gave a basis for comparison of different radiation dosage patterns in different centres, and generated worldwide acclaim. It led to visiting professorial appointments at centres in the US, including nine months at the University of Southern California, 30 months in Wisconsin and a further 30 months at the Memorial Sloane-Kettering Institute in New York. In New York he was told, to confirm his credentials, that he should put his medical qualifications up in his office. Lacking the paperwork, he put the cheque from the cycle ride up instead. Well after his final retirement in 1980, he continued to lecture and to publish scientific papers.

Throughout his life he believed strongly in progress - and peace - through reasoned argument. A lifelong Christian, upon his arrival in Oxford he joined the Quaker Society of Friends and was active in the local United Nations association. He considered the NHS a triumph of national policy. These parts of his philosophy are summed up in the final verse of a long poem he wrote (and sang!) at a scientific meeting held in his honour in his 95th year: "And now I'll sing the last verse / With what's most on my mind / I hope that human beings / Have sense to save their kind / By letting their behaviour / Be led by common sense/ And reason be their saviour / Instead of violence."

Frank was one time president of the British Institute of Radiology. He was awarded the Gold Medal of the Royal College of Radiologists. He received an OBE in the Millennium New Year Honours for his contributions to cancer services over much of the 20th century. In his 100th year, he received in person a Sheffield University honorary doctorate.

To him, every patient was a new challenge to improve upon his previous treatments. This did not always find favour with colleagues, who preferred the security of standard protocols. But it inspired his trainees and achieved excellent results for many. When at medical school, Frank was known as Tiger Ellis, a nickname which sums up his energy, drive and knack for inspiring those who worked with him.

Dorothy predeceased him. He was very proud of his family and 28 of its members survive him including five children, 13 grandchildren and great-grandchildren.

· Frank Ellis, clinical oncologist, born August 22 1905; died February 3 2006